PROJECT SUMMARY/ABSTRACT (GNOTOBIOLOGY CORE) Gnotobiology (meaning ?known life?) is the science of animals that are devoid of microbes (germ-free) or associated with defined microbial consortia. Experiments involving gnotobiotic zebrafish are central to each of the Research Projects of this Program Project Grant. The Gnotobiology Core provides the expertise necessary to ensure that experiments described in this proposal are carried out with maximal efficiency and minimal unnecessary use of vertebrate animals. Beyond ensuring that established methods of germ-free derivation and gnotobiotic experimentation are implemented to guarantee the highest level of quality control, the Gnotobiology Core will carry out research that extends the limits of our current gnotobiotic husbandry methodologies. These research objectives include extending the period of time over which germ-free zebrafish can be maintained, developing new ways to co-house zebrafish to control the inter-individual transmission of their microbes, and increasing the range and type of experiments that can be performed with zebrafish- associated microbes through developing and implementing new genetic engineering strategies in bacteria. Achieving these objectives will significantly enhance the ability to carry out experiments described in the Research Projects.